Time series of atmospheric Δ¹⁴CO₂ recorded in tree rings from Northwest China (1957-2015)

Radiocarbon (¹⁴C) is a unique and important tool for understanding carbon cycle in the nature, and its use can be significantly enhanced where reliable historical atmospheric Δ¹⁴CO₂ records can be established. In China, continuous atmospheric Δ¹⁴CO₂ records since the 1950s are scarce, a period when dramatic variations of Δ¹⁴CO₂ occurred caused by intensive human activities. In this research, Δ¹⁴C of Qinghai spruce tree rings collected from Huangzhong (HZ) (36.27°N, 101.67°E, 2982 m amsl) were measured by Accelerator Mass Spectrometry, and a Δ¹⁴CO₂ time series from 1957 to 2015 was reconstructed. The results show that HZ Δ¹⁴C was generally higher than the contemporaneous average level in the mid-high latitudes of the Northern Hemisphere. The peak value of HZ Δ¹⁴C occurred in 1964 (as bomb peak) was higher than that of other tree ring records in East Asia at a similar latitude, likely due to the impact of the atmosphere nuclear tests at Semipalatinsk (Kazakhstan). The record shows no obvious disturbance of Lop Nor nuclear weapons tests (in Northwest China) during 1964-1980, except for 1971. A local Suess effect began to appear since 2001, and the estimated atmospheric fossil fuel-derived CO₂ (CO_2ff) concentration increased from 3.5 ppm to 8.8 ppm from 2006 to 2015. This is associated with the implementation of the "Western Development" strategy in China. HZ Δ¹⁴C records document background Δ¹⁴C data, useful for regional carbon cycle research and atmospheric CO_2ff quantification in the region. These data also provide baseline values for assessment environmental safety connected with nuclear power plants in China.